Metalized film capacitor

ABSTRACT

The present invention is to provide a metallized film capacitor having a compact size, a large capacitance and a low inductance whereas number of parts is reduced. The metallized film capacitor comprises: a plurality of capacitor elements ( 1 ) provided with metallized contact electrodes ( 2 ) on both ends in the width direction; a bus-bar ( 3 ) to connect each of a plurality of electrodes ( 2 ) on one end; and a capacitor case ( 5 ) to house a plurality of capacitor elements ( 1 ), wherein a plurality of capacitor elements ( 1 ) are arranged in the capacitor case such that one side of electrodes ( 2 ) faces the opening surface of capacitor case ( 1 ) and each electrode ( 2 ) of one of both ends of each capacitor element ( 1 ) are positioned generally coplanarly.

TECHNICAL FIELD

The present invention relates to a metallized film capacitor used forelectronic, electrical and industrial equipment, vehicles or the likeand particularly to a smoothing capacitor for use in an inverter circuitfor motor starting installed in hybrid vehicles or the like.

BACKGROUND ART

The metallized film capacitor, although having a disadvantage of largevolume compared with the aluminum electrolytic capacitor of anequivalent amount of capacitance, has excellent properties of lowlosses, high withstand voltage, low temperature and frequency dependencyor the like. Particularly the film capacitor can work well under highvoltages of DC 500 V or higher if the film thickness is controlledsuitably due to a high withstand voltage of the dielectric film.

Contrarily the aluminum electrolytic capacitor is difficult for use onDC 500 V or higher due to restrictions of the withstand voltage of thedielectric oxide film. To use the aluminum electrolytic capacitor for ahigh voltage application, therefore, a plurality of aluminumelectrolytic capacitors must be connected in series to share the voltageapplied.

In addition to this, the aluminum electrolytic capacitors connected inseries need in operation to connect a resistor in parallel with thecapacitors to maintain the voltage applied on each resistor to a certainvalue. The metallized film capacitor has been widely used for highvoltage of DC 500 V or higher, even in a case of DC circuit, because thealuminum electrolytic capacitor is difficult to use on a high voltageapplication as mentioned above.

Such conventional technologies are disclosed for instance in JapanesePatent Laid-Open Application No. H08-31690 and 2001-76967. Themetallized film capacitor is used for various purposes such as filteringin DC circuits, smoothing in inverter circuits or the like. A pluralityof capacitors connected in parallel is generally used to increase thecapacitance if a single capacitor element itself cannot provide enoughcapacitance.

However, a plurality of single metallized film capacitors connected inparallel occupies a large space. Additional problem is that manybus-bars are necessary for connection, causing an increase in productcost.

Another problem is that electrical connection using many bus-bars causesa long wiring length, resulting in a large total inductance.

A method to include a plurality of capacitor elements connected inparallel in a case has been disclosed, but any method to maximize thearrangement of the capacitor elements in the case is not yet disclosed.

Moreover, in a hot and humid environment possible in a hybrid car or thelike, moisture gradually enters during operation from a resin surface ofthe case opening. This will cause eventually a deterioration ofevaporated metals on the film and will decrease the capacitance greatlywith time.

To solve the problems mentioned above, the present invention aims atproviding a metallized film capacitor with a compact size, a largecapacitance, a low inductance and a reduced number of parts.

DISCLOSURE OF THE INVENTION

The present invention is to provide a metallized film capacitorcomprising: a plurality of capacitor elements composed of rolled up ormulti-layered metallized films and provided with electrodes on both endsin the width direction; a bus-bar to connect each electrode of aplurality of the capacitor elements; and a capacitor case (case) toinclude a plurality of the capacitor elements, wherein a plurality ofthe capacitor elements are arranged to face a same direction in thecase, placing each electrode of both ends generally coplanarly.

Additionally, a metallized film capacitor comprising: a plurality ofcapacitor elements composed of rolled up or multi-layered metallizedfilms and provided with electrodes on both ends in the width direction;an electric conductor to connect each electrode of a plurality of thecapacitor elements; and a case to include a plurality of the capacitorelements, wherein the capacitor case houses a plurality of the capacitorelements having different widths of the metallized film and eachelectrode of each capacitor elements is connected in parallel so as tosandwiched between two pieces of bent electrical conductors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of the metallized film capacitor used inexemplary embodiment 1 of the present invention.

FIG. 2 shows a manufacturing process of the flattened capacitor elementused in exemplary embodiment 1 of the present invention.

FIG. 3A shows a top view of the metallized film capacitor used inexemplary embodiment 2 of the present invention.

FIG. 3B shows a sectional side view of the metallized film capacitorused in exemplary embodiment 2 of the present invention.

FIG. 4A shows a top view of the metallized film capacitor used inexemplary embodiment 3 of the present invention.

FIG. 4B shows a sectional side view of the metallized film capacitorused in exemplary embodiment 3 of the present invention.

FIG. 5A shows a top view of the metallized film capacitor used inexemplary embodiment 4 of the present invention.

FIG. 5B shows a sectional side view of the metallized film capacitorused in exemplary embodiment 4 of the present invention.

FIG. 6A shows a top view of the metallized film capacitor used inexemplary embodiment 5 of the present invention.

FIG. 6B shows a sectional side view of the metallized film capacitorused in exemplary embodiment 5 of the present invention.

FIG. 7A shows a top view of the metallized film capacitor used for acomparative example.

FIG. 7B shows a sectional side view of the metallized film capacitorused for a comparative example.

DETAILED DESCRIPTIONS OF THE INVENTION

The exemplary embodiments in the present invention are described withreference to drawings. The drawings do show schematically only positionsof elements and do not show dimensions correctly.

Exemplary Embodiment 1

Capacitor 1 is formed of two sheets of metallized film 21, evaporated onone side, rolled up and flattened using a polypropylene film as thedielectric as shown in FIG. 2. Metallized film 21 of capacitor 1 isprovided with metallized contact electrodes formed by zinc spraying onboth ends in the width direction. A pair of elongated copper bus-bars 3,electrical conductors, connect each metallized contact electrode 2 of aplurality of capacitors 1 on both ends. Bending the ends of bus-bars 3provides electrode terminals 4 for external connection. That is,electrode terminals 4 are integrated with bus-bars 3.

Capacitor case (case) 5 is formed from polyphenylene-sulfide (PPS).Instead of plastics such as PPS or polybutylene terephthalate (PBT),metals such as aluminum can be available for the case material. Aplurality of capacitors 1 are aligned in case 5, appressed againstflattened surfaces la toward a same direction, as shown in FIG. 1. Beingpositioned each metallized contact electrode of a plurality ofcapacitors 1 on each of both ends generally coplanarly, one side facesthe opening surface and the other side faces the bottom surface of case5. A pair of bus-bars 3 connect each metallized contact electrode 2 ofcapacitors 1 facing the opening surface and facing the bottom surface ofcase 5. Empty spaces of case 5 thus including a plurality of capacitorelements 1 and a pair of bus-bars 3 are filled with epoxy resin 8 as asealant (shown partially by hatching in FIG. 1). The configuration canimprove reliabilities of the capacitor such as moisture resistance orthe like. The electrostatic capacitance (capacitance) of the metallizedfilm capacitor shown in FIG. 1 that includes 6 flattened capacitorelements 1 connected in parallel by using a pair of bus-bars 3 is thesum of capacitance of 6 capacitor elements 1. A single capacitor element1 has an amount of capacitance of 70 μF, resulting in an amount ofcapacitance of 420 μF totally.

Metallized contact electrodes 2 of respective capacitor elements 1 arepositioned coplanarly and are connected to bus-bars 3 in the level bysoldering. One of metallized contact electrodes 2 faces the openingsurface, and the other the bottom surface of case 5.

Case 5 is 105 mm wide, 60 mm long, and 60 mm high, and bus-bar 3 is 1 mmthick.

Electrode terminal 4 protrudes externally by 30 mm from the surface offilled epoxy resin 8 of case 5.

Next, the manufacturing method of flattened capacitor element 1 for themetallized film capacitor in exemplary embodiment 1 is described withreference to FIG. 2. To make flattened capacitor element 1, firstly twosheets of metallized film 21 consisting of polypropylene film of 3.2 μmthick, aluminum evaporated on one side, are rolled up around roll core 7(core diameter of 20 mm) to form a cylindrical convolute body 6.

The present invention does not so limit the core diameter of 20 mm asadopted in exemplary embodiment 1. The core diameter should preferablybe large with respect to the size of case 5 to increase the flatteningratio of the capacitor element. The capacitor element thus formed canutilize the space of case more efficiently as many capacitor elementscan be aligned in case 5, appressed against flattened surfaces 1 atoward a same direction.

Next, roll core 7 is removed from the cylindrical convolute body 6 ofmetallized films. Pressing vertically the cylindrical convolute body 6forms a flattened convolute body 6, and subsequently zinc thermalspraying can provide both ends of the flattened convolute body 6 withmetallized contact electrodes 2 to complete flattened capacitor element1. The flattened form of the element can utilize the space of case 5more efficiently. The two sheets of metallized film 21 with aluminumevaporated on one surface to produce capacitor element 1 is provided onone edge in the width direction with narrow margins 22 free of theevaporated film, as is well known in the conventional metallizedcapacitors. By rolling convolutedly in two metallized films in thedirection such that margin 22 does not meet each other, the metallizedfilm capacitor can be provided with metallized contact electrodes 2extended from each of both ends. The present invention does not so limitthe dielectric film, kinds of the evaporated metal, materials of thebus-bars, and materials of capacitor case (case) to such as adopted inexemplary embodiment 1. PBT or PPS may be agreeable for dielectricfilms. Zinc, an aluminum-zinc alloy or the like may be acceptable foruse in the metalization. Copper, copper plated parts, aluminum or thelike can be used for the bus-bar.

Table 1 lists capacitance per unit volume (μF/cm³), inductance (nH) andrate-of-change of capacitance (%) of the metallized film capacitor usedin exemplary embodiment 1 of the present invention. Where, therate-of-change of capacitance is a ratio of change in capacitance, afterloading DC 600 V for 2000 hours continuously in an ambient of atemperature of 85° C. and a relative humidity of 85%, to an initialcapacitance expressed in percentage.

Exemplary Embodiment 2

The metallized film capacitor used in exemplary embodiment 2 is mainlydescribed on the points different from exemplary embodiment 1, as thebasic configuration and functional effects of the metallized filmcapacitor are similar to those of exemplary embodiment 1, thereforesimilar elements have the same reference marks and detailed descriptionsare omitted.

The size of case 5 is 160 mm wide, 120 mm long, and 75 mm high, andbus-bar 3 a to connect metallized contact electrodes 2 has a plate-likesize so as to cover the opening of case 5 as shown in FIGS. 3A and 3B.Moreover, case 5 is designed to include 24 pieces of capacitor elements1 in case 5 by changing rolling numbers of metallized films 21 and thediameter of roll core 7. Twenty-four pieces of capacitor elements 1 arehoused in case 5 arranged in a plurality of lines along with a certaindirection. The single flattened capacitor element 1 has a capacitance of58.3 μF, resulting a large amount of capacitance of 1400 μF in thecapacitor totally. Table 1 lists capacitance per unit volume (μF/cm³),inductance (nH) and rate-of-change of capacitance (%) of the metallizedfilm capacitor used in exemplary embodiment 2 of the present invention.The definition of the rate-of-change of capacitance is the same as forexemplary embodiment 1.

Exemplary Embodiment 3

The metallized film capacitor used in exemplary embodiment 3 is mainlydescribed on the points different from exemplary embodiment 1, as thebasic configuration and functional effects of the metallized filmcapacitor are similar to those of exemplary embodiment 1, thereforesimilar elements have the same reference marks and detailed descriptionsare omitted.

Exemplary embodiment 3 employs capacitor case (case) 1 a having tallerside surface in left-hand half than in right-hand half, an uneven sideview, as shown in FIG. 4B that is a modification of the case used inexemplary embodiment 2.

The flattened capacitor element 1 has two kinds of capacitor elementhaving different widths of the metallized film. The taller left-handhalf of case 5 a houses taller capacitor elements 1 formed of widermetallized films 21. The lower right-hand half of case 5 a houses lowercapacitor elements 1 formed of narrower metallized films 21. Everycapacitor element 1 is housed in case 5 a, putting one of metallizedcontact electrodes 2 on the bottom surface coplanarly. The flattenedcapacitor elements 1 thus housed cause a difference in height in bothsides of the centerline of the opening of case 5 a accordingly.

Additionally, bus-bars 3 a located in the opening side of case 5 a toconnect metallized contact electrodes 2 are bent in the center toconnect metallized contact electrode of every capacitor element 1 inparallel as shown in FIG. 4B.

The volume of case 5 s of exemplary embodiment 3 is the sum of tworectangular solids of:

80 mm wide, 120 mm long, and 75 mm high, and

80 mm wide, 120 mm long, and 100 mm high.

This amounts to 1680 cm³ totally.

The single flattened capacitor element 1 has a capacitance of 58.3 μFfor narrow type and 78 μF for wide type respectively, resulting in alarge amount of capacitance of 1635 μF in the metallized film capacitortotally. Table 1 lists capacitance per unit volume (μF/cm³), inductance(nH) and rate-of-change of capacitance (%) of the metallized filmcapacitor used in exemplary embodiment 3 of the present invention. Thedefinition of the rate-of-change of capacitance is the same as forexemplary embodiment 1.

Exemplary Embodiment 4

The metallized film capacitor used in exemplary embodiment 4 is mainlydescribed on the points different from exemplary embodiment 1 and 2, asthe basic configuration and functional effects of the metallized filmcapacitor are similar to those of exemplary embodiment 1 and 2,therefore similar elements have the same reference marks and detaileddescriptions are omitted.

In exemplary embodiment 2, eight pieces of the flattened capacitorelement 1 are aligned in a same positioning in all of the three lines.Contrarily, the flattened capacitor elements 1 are arranged in a zigzagformation to reduce dead spaces as much as possible in exemplaryembodiment 4 as shown in FIG. 5A. The central line consists of sevenpieces of capacitor elements 1 having an amount of capacitanceequivalent to the other sides and additional two pieces of capacitorelements 1 b having an amount of one half of the capacitance. Theabovementioned arrangement of capacitor elements 1 and 1 b will be ableto utilize dead spaces D in FIG. 3A efficiently. The configuration canincrease the amount of capacitance per each capacitor element 1 by 7%,and consequently can provide the metallized film capacitor with 1500 μF.Table 1 lists capacitance per unit volume (μF/cm³), inductance (nH) andrate-of-change of capacitance (%) of the metallized film capacitor usedin exemplary embodiment 4. The definition of the rate-of-change ofcapacitance is the same as for exemplary embodiment 1.

Exemplary Embodiment 5

The metallized film capacitor used in exemplary embodiment 5 is mainlydescribed on the points different from exemplary embodiment 1 to 4:using of multi-layered capacitor elements. The basic configuration andfunctional effects of the metallized film capacitor are similar to thoseof exemplary embodiment 1 to 4, therefore similar elements have the samereference marks and detailed descriptions are omitted.

Multi-layered capacitor element 9 shown in FIGS. 6A and 6B replacesflattened capacitor elements 1 used in exemplary embodiments 1 to 4.

Multi-layered capacitor element 9 can be produced by cutting to removecorner (curved) portions of flattened capacitor element 1, used inexemplary embodiments 1 to 4, perpendicularly to metallized contactelectrode 10.

Irradiations of YAG laser can remove evaporated metals on the cutsurfaces and can apply a withstand voltage in the cut surfaces. Use ofsuch multi-layered capacitor elements can reduce the dead spaces incapacitor case (case) 5 drastically. The capacitance of the metallizedfilm capacitor amounts to 1860 μF.

Table 1 lists capacitance per unit volume (μF/cm³), inductance (nH) andrate-of-change of capacitance (%) of the metallized film capacitor usedin exemplary embodiment 5. The definition of the rate-of-change ofcapacitance is the same as for exemplary embodiment 1.

Comparative Example

The comparative example is described with reference to FIGS. 7A and 7B.In the comparative example, flattened capacitor elements 1 are arrangedsuch that metallized contact electrodes 2 face perpendicularly to thebottom surface of case 5. Six pieces of bus-bars 11 connect metallizedcontact electrodes 2 as shown in dotted lines and solid lines in FIG.7A. The metallized film capacitor is completed after connecting twopieces of bus-bars additionally as electrode terminals 4.

The number of bus-bars used in the comparative example amounts to 8pieces totally. Costs of bus-bars doubles compared with exemplaryembodiments 1 to 5 that use only two pieces of bus-bars, and yet theamount of capacitance is only 1200 μF. Moreover, the amount ofcapacitance per unit volume becomes smaller compared with exemplaryembodiment 2 to 4 due to an adequate clearance between oppositepolarities of bus-bars 11.

Table 1 lists capacitance per unit volume (μF/cm³), inductance (nH) andrate-of-change of capacitance (%) of the metallized film capacitor usedin the comparative example. The definition of the rate-of-change ofcapacitance is the same as for exemplary embodiment 1. TABLE 1Capacitance per Rate-of-change of Exemplary unit volume Inductancecapacitance embodiment (μF/cm³) (nH) (%) 1 1.11 25.6 −4.9 2 0.972 23.5−2.0 3 0.974 25.1 −2.3 4 1.04 23.2 −2.2 5 1.29 19.5 −3.5 Comparative0.833 42.3 −9.8

The comparative example has a longer wiring distance compared withexemplary embodiment 1 to 5 due to extended length of bus-bars 11,causing an increase in inductance.

The comparative example has a larger rate-of-change of capacitancecompared with exemplary embodiment 2 to 5, as copper-made bus-bar 3 a toprevent moisture ingress is not provided on the resin surface of theopening. The copper-made bus-bars 3 of exemplary embodiment 1 is not solarge as enable to cover the opening compared with exemplary embodiment2 to 5, causing an increase in rate-of-change of capacitance.

As mentioned above, forming a plate-like bus-bar 3 so as to cover theopening of the case can improve moisture resistance of the metallizedfilm capacitor.

INDUSTRIAL APPLICABILITY

The present invention can provide a metallized film capacitor with astructure easy for downsizing, with increasing in capacitance and areduced cost and a strong moisture resistance. The metallized filmcapacitor can operate in electronic, electrical and industrial equipmentunder possible hot and humid environments.

1. A metallized film capacitor comprising: a plurality of capacitorelements composed of rolled up or multi-layered metallized films andprovided with electrodes on both ends in the width direction; anelectrical conductor to connect each of the electrodes of each end of aplurality of the capacitor elements; and a capacitor case to house aplurality of the capacitor elements, wherein a plurality of thecapacitor elements are aligned facing a same direction in the capacitorcase, placing each of the electrodes of each end generally coplanarly,and further using a resin as a sealant to house a plurality of thecapacitor elements into the capacitor case.
 2. A metallized filmcapacitor comprising: a plurality of capacitor elements composed ofrolled up or multi-layered metallized films and provided with electrodeson both ends in the width direction; an electrical conductor to connecteach of the electrodes of each end of a plurality of the capacitorelements; and a capacitor case to house a plurality of the capacitorelements, wherein the capacitor case houses, using a resin as a sealant,a plurality of the capacitor elements having different widths of themetallized film and each of the electrodes of each of the capacitorelements is connected in parallel so as to sandwiched between two piecesof the bent electrical conductors.
 3. The metallized film capacitor ofclaim 1, wherein the electrical conductors to connect each of theelectrodes have a plate-like form and integrated with electrodeterminals, and portions to be the electrode terminal protrudesexternally from the capacitor case.
 4. The metallized film capacitor ofclaim 2, wherein the the electrical conductors to connect each of theelectrodes have a plate-like form and integrated with electrodeterminals, and portions to be the electrode terminal protrudesexternally from the capacitor case.
 5. The metallized film capacitor ofone of claim 1, wherein the capacitor element is formed flattened. 6.The metallized film capacitor of claim 2, wherein the capacitor elementis formed flattened.
 7. The metallized film capacitor of claim 1,wherein: the capacitor case formed a rectangular solid has an openingsurface and a bottom surface facing the opening surface; and thecapacitor elements are arranged such that one of the electrodes face theopening surface and another of the electrodes face the bottom surfacerespectively and are aligned toward a same direction.
 8. The metallizedfilm capacitor of claim 2, wherein: the capacitor case formed arectangular solid has an opening surface and a bottom surface facing theopening surface; and the capacitor elements are arranged such that oneof the electrodes face the opening surface and another of the electrodesface the bottom surface respectively and are aligned toward a samedirection.
 9. The metallized film capacitor of claim 1, wherein: thecapacitor case formed a rectangular solid has an opening surface and abottom surface facing the opening surface; and the capacitor elementsare arranged such that one of the electrodes faces the opening surfaceand another of the electrodes faces the bottom surface respectively andare aligned in a plurality of lines toward a same direction.
 10. Themetallized film capacitor of claim 2, wherein: the capacitor case formeda rectangular solid has an opening surface and a bottom surface facingthe opening surface; and the capacitor elements are arranged such thatone of the electrodes faces the opening surface and another of theelectrodes faces the bottom surface respectively and are aligned in aplurality of lines toward a same direction.
 11. The metallized filmcapacitor of claim 9, wherein a plurality of the capacitor elements arearranged in a zigzag formation toward a same direction.
 12. Themetallized film capacitor of claim 10, wherein a plurality of thecapacitor elements are arranged in a zigzag formation toward a samedirection.
 13. The metallized film capacitor of claim 1, wherein thecapacitor element has a form of a generally rectangular solid ofmulti-layered capacitor by cutting to remove both side corner portionsof the flattened capacitor element perpendicularly to the electrode. 14.The metallized film capacitor of claim 2, wherein the capacitor elementhas a form of a generally rectangular solid of multi-layered capacitorby cutting to remove both side corner portions of the flattenedcapacitor element perpendicularly to the electrode.
 15. The metallizedfilm capacitor of claim 1, wherein the electrical conductor to connectthe electrodes facing the opening surface of the capacitor case isformed plate-like so as to cover the opening.
 16. The metallized filmcapacitor of claims 2, wherein the electrical conductor to connect theelectrodes facing the opening surface of the capacitor case is formedplate-like so as to cover the opening.